Halogenated hydrocarbons have found widespread use in a variety of industrial applications, including as refrigerants, aerosol propellants, blowing agents, heat transfer media and gas dielectrics. Many of these applications have heretofore utilized compositions comprising major amounts of chlorofluorocarbons (“CFCs”) and hydrochlorofluorocarbons (“HCFCs”). However, suspected environmental problems have become associated with the use of some of these halogenated hydrocarbons. For example, both CFCs and HCFCs tend to exhibit relatively high global warming potentials. Accordingly, it has become desirable in many applications to use compositions which are otherwise acceptable for the intended use but which at the same time have lower global warming potentials than CFCs and other disfavored halogenated compounds.
Applicants have recognized that certain compositions comprising iodinated compounds, and in particular, compositions comprising trifluoroiodomethane, may be used advantageously to replace various chlorinated compounds, many of which have high global warming potentials, in refrigeration (and other) applications to reduce potential environmental damage caused thereby. Applicants have further recognized, however, that iodinated compounds, such as trifluoroiodomethane, tend to be relatively unstable, and often significantly less stable than CFCs, HCFCs and hydrofluorocarbons (HFCs), especially under certain conventional refrigeration conditions.
To be useful as refrigerants and replacements for other CFC, HCFC and HFC fluids, suitable compositions comprising iodinated compounds must be stabilized. Applicants have recognized one possible way to produce suitable stable iodo-compositions is to use stabilizing compounds therein.
A variety of stabilizers for use with HCFC and CFC compositions are known. HFCs, due to their exceptional stability, may or may not use stabilizers incorporated in their compositions as known in the art. For example, U.S. Pat. No. 5,380,449 discloses compositions comprising dichlorotrifluoroethane and stabilizing amounts of at least one phenol and at least one aromatic or fluorinated alkyl epoxide. However, because iodo-compounds tend to be significantly less stable that CFCs and HCFCs, it cannot be predicted from teachings of stabilizers for CFCs and HCFCs (e.g. the '449 disclosure) whether the same or similar compounds are capable of stabilizing iodo-compounds to a sufficient degree for use as CFC/HCFC replacements. That is, as will be recognized by those of skill in the art, C—Cl and C—F bonds tend to be at least about 1.5-2 times stronger than C—I bonds. Accordingly, it is neither inherent nor necessarily reasonable to expect that a compound that stabilizes an HCFC or CFC will be suitable for an iodo-compound which requires about twice the amount of added stability to be useful in refrigerant applications.
Applicants have thus recognized the need to produce compositions comprising iodo-compounds, such as trifluoroiodomethane, that are sufficiently stable for a variety of uses including as replacements for CFC, HCFC and HFC refrigerants.
It has been proposed to utilize certain iodocarbon compounds in refrigeration applications as replacements for certain of the CFCs and HCFCs that have heretofore been used. For example, Japanese Kokai 09-059612 (Application No. 07-220964) discloses refrigerant compositions comprising trifluoroiodomethane and one or more phenolic compounds. This patent document indicates that the phenolic compositions act to stabilize the trifluoroiodomethane against degradation.
While the compositions containing phenolic compounds as stabilizers for trifluoroiodomethane may enjoy a certain degree of success, in certain applications it may be desirable to not use phenolic compounds or to use such compounds in a lower concentration. For example, phenols are generally acidic due to the dissociability of the hydroxyl group and are relatively reactive. These characteristics may be undesirable in certain applications and/or in certain situations.